A 64-bit version of Windows 7 can access from 1 GB of RAM to more than 128 GB of RAM.

Memory access per edition

All 32-bit versions of Windows 7 can access up to 4 GB of RAM.

Windows 7 Home Basic - 8 GB of RAM

Windows 7 Home Premium - 16 GB of RAM

Windows 7 Ultimate - 128 GB of RAM or more

DEP

32-bit versions of Windows 7 use a software-based version of DEP.

64-bit versions of Windows 7 support hardware-backed DEP.

Kernel Patch Protection (PatchGuard)

This feature is not available in 32-bit versions of Windows 7

This feature is available in 64-bit versions of Windows 7. Kernel Patch Protection helps prevent a malicious program from updating the Windows 7 kernel. This feature works by helping to prevent a kernel-mode driver from extending or replacing other kernel services. Also, this feature helps prevent third-party programs from updating (patching) any part of the kernel.

Driver signing

Unsigned drivers may be used with 32-bit versions of Windows 7.

64-bit versions of Windows 7 require that all device drivers be digitally signed by the developer.

32-bit driver support

32-bit versions of Windows 7 support 32-bit drivers that are designed for Windows Vista.